Conventional mechanically operated tire curing presses utilize large side plates on either side of a base which include cam slots for the movement of trunnions on opposite ends of a significant beam operated by links connected to bull gears on the outside of each side plate. The bull gears are usually driven by a substantial electric motor through a worm gear reduction drive. The beam beneath which the upper mold sections are supported, the links, the bull gears and the mechanical drive are utilized to hold the press closed to resist the significant internal pressures achieved during tire curing.
The beam, side plates, links and bull gears together with the drive for the bull gears add significantly to the weight of the press not to mention its cost. Moreover, the beam, links, side plates and bull gears significantly add to the envelope of the press requiring substantial space and height, particularly for presses of large size. Moreover, the above-noted components of a mechanical press not only limit access to the mold cavities but also tend to restrict the amount and type of insulation which can be provided around the mold cavity thus, in reality, enhancing the energy inefficiency of a conventional tire press.
Attempts have been made to eliminate the abovenoted components of the usual mechanical press and reference may be had to Cantarruti U.S. Pat. No. 4,025,251 entitled VULCANIZER LOCK MEANS, for an example. However, even with a lock such as a rotating bayonet ring, the internal pressures of the press tend to distort the mold parts in the absence of a high pressure preloading clamp which is normally achieved by the aforenoted components in a mechanical press. Thus, under such pressures the mold sections may actually tend to dish or become concave, particularly in the area of the center mechanism, requiring reactant clamping forces. Also, high clamping pressures over the entire mold or platen area restricts the amount and type of insulation employed, which in conventional presses may require frequent replacement. If the area of application of the clamping forces can be reduced, more efficient insulation can be used around the mold obtaining a more energy efficient cure. Attempts have been made to solve some of the noted problems with hydraulic presses. However, because of the high heat involved in tire curing and the deleterious effect that hydraulic fluid has on uncured or cured rubber, such attempts have not generally met with success.
For example, in some hydraulic presses the high heat involved has so degraded the hydraulic fluid used for clamping pressures that such fluid has been required almost continually to be replaced. Moreover, if hydraulic leaks develop, which is to be expected, any leaking fluid which may fall on either an uncured tire or a hot cured tire leaving the press can result in a scrap tire.
Accordingly, it is highly desirable to provide a tire press eliminating the mechanical components noted above but providing fluid operating components together with a mechanical lock with such components being positioned either beneath or laterally offset from the path of the uncured and then cured tire through the press. Moreover, if hydraulic fluid is employed, it is important to isolate the hydraulic fluid of the system from the high heat of the curing operation. It is also important in a fluid operated or hydraulic press to provide a mechanical blocking system which will preclude the mold parts from separating significantly in the event of the loss of hydraulic or fluid pressure.